Ventilation and cooling control system for modular platforms

ABSTRACT

A platform for holding a plurality of modules or printed circuit boards wherein the platform or chassis contains shutters placed over airflow openings in the platform. The shutters are normally closed and are opened by the act of inserting a module into the platform. The shutters are in the closed position in all slots not occupied by a module and are in the open state in all slots populated by a module. The shutters open as the module is inserted and close when the module is removed. The closed shutters prevent airflow from passing through the unpopulated slots and empty space within the platform, thus forcing the airflow to pass through the space in which the modules are present. The platform also comprises a means of controlling the number of fans that are operational in accordance with the number of modules installed in the platform. The fans closest to the modules inserted into the platform are operational while fans close to unpopulated slots are turned off. A switch or electrical contacts in the rear of the modules can be used to control the operation of the fans. In an alternative embodiment, the lower and/or the upper portion of the chassis comprises one or more one time twist off tabs for each slot that extend from the front to the rear of the platform. The twist off tabs for a slot are left intact for a slot not to be populated with modules. The tabs are removed for slots to be populated with a module.

FIELD OF THE INVENTION

The present invention relates generally to modular platform design andmore particularly relates to a system for controlling the ventilationand cooling within a modular platform such as a card cage.

BACKGROUND OF THE INVENTION

It is and has been common practice in the engineering field to constructlarge electronic systems from a plurality of printed circuit (PC) boardsor PCBs that are arranged and installed in one or more card cages orchassis. The card cages are typically constructed from metal or someother sturdy material and serve to mechanically support the multitude ofelectrical PC boards making up the apparatus. Each card in the cageplugs into a backplane which may be either passive or active.

The card cages typically contain a variable number of PC boards orcards, i.e., electronic and electrical modules, generally referencedmodules. The card cages are designed to provide a plurality of functionsto the modules contained therein. As stated above, the major functionprovided is mechanical support for all the cards to be placed in thecage. Also, the cage serves to provide a mounting means for thebackplane which ties all the cards together. The cage also providesmeans for the mounting of the power supply which may consist of morethan one unit. In addition, the cage provides the means for managementof configuration and functional parameters support. The cage furthersupports any other service or functional support required by the PCBsenclosed therein. Card cages or boxes that provide one or more servicesto the PC boards are also termed platforms, as used in the descriptionhereinbelow.

In the typical scenario, platforms for a multiple number of modulesnormally generate large quantities of heat that must be removed. Themost common method for the removal of this heat is forced airventilation by means of one or more electrical fans. The use of forcedair ventilation has, however, a number of disadvantages and drawbacksthat must be considered when the removal of heat is accomplished bysimply installing fans in the platform.

First, the number of modules installed in the platform may vary betweena minimum of none to the maximum number available in the givenparticular platform. The air flow path can change in accordance with thenumber of modules installed in the platform. In many cases, the air flowpath can change in such a way that one or more modules present in theplatform receive a minimal of cooling while most of the air flow passesunused through the spaces or slots unoccupied by modules. In such cases,the designers of the platforms usually increase the airflow by asignificant amount in order to provide sufficient cooling to make theworst case scenario of possible combinations of present and absentmodules still acceptable.

This prior art approach suffers from several disadvantages as describedbelow. First, increasing the airflow requires additional fans and eachfan must have increased capacity. It is not guaranteed, however, thateach platform will have sufficient room to accommodate the larger numberof fans required by this approach.

Second, the increased number of fans generates additional noise. In mostcountries, platforms are required to comply with government regulationsand/or standards limiting noise production. The use of powerful fans, inlarge numbers, makes compliance with statutory or standards based noiselimitations more difficult if not practically impossible.

Third, high capacity fans typically operate under increased stress. Itis thus highly probable that these larger capacity fans will have lowerMean Time Between Failure (MTBF) ratings.

Fourth, additional fans, especially higher airflow capacity fans,require significant additional power from the electrical power plant inthe platform.

An illustrative example of this problem will now be presented. Take, forexample, a 16 slot card chassis that can host as few as a single moduleor as many as 16 modules. In cases when most of the space inside thechassis is not occupied by modules, the airflow may pass through thefree space leaving a single module almost or completely without coolingairflow. In particular, consider a platform, i.e., chassis, with eightmodules placed on one side of the platform. In such an arrangement, theairflow is severely reduced within the area populated by modules, whichis the area in need of cooling. Most of the airflow takes the path ofleast resistance, which is the unpopulated portion of the platform. Inorder to provide sufficient cooling to the modules, the designer of theplatform of this example, must place six fans, each providing 50 cfm. Inthe case when all 16 modules are inserted in the platform, only 30 cfmper fan is sufficient to provide adequate cooling.

Thus, there is a strong felt need for a platform (card chassis) thatconsumes less power, generates less noise, does not lower the MTBF ofthe fans installed therein and which is able to supply cooling airflowto the modules (PCBs) that are installed therein regardless of thenumber of modules installed and their position in the platform.

SUMMARY OF THE INVENTION

The present invention is a platform for holding a plurality of modulesor printed circuit boards (PCBs) wherein the platform or chassiscontains shutters that are placed over airflow openings in the platform.These shutters are normally closed and are opened by the act ofinserting a module into the platform. Thus, the shutters are in theclosed position in all slots unoccupied by a module and are in the openstate in all slots populated by a module. The shutters are operatedmechanically by the act of inserting the modules into the platformchassis. The shutters open as the module is inserted and close when themodule is removed. The shutters that are closed function to preventairflow from passing through the unoccupied slots and empty space withinthe platform, thus forcing the airflow to pass through the space inwhich the modules are present. This serves to greatly improve thecooling efficiency of the platform for any given fan capacity.

In addition, the platform of the present invention comprises a means ofcontrolling the number of fans that are operational in accordance withthe number of modules installed in the platform. The fans closest to themodules inserted into the platform shall be operational. Conversely,fans close to unpopulated slots shall be turned off. A switch orelectrical contacts in the rear of the modules can be used to controlthe operation of the fans. Controlling the operation of the fans inaccordance with the position and number of installed modules serves toimprove the availability of the cooling system due to the fact thatinactive fans lengthen the effective MTBF rating of the fans.

In an alternative embodiment, the lower and/or the upper portion of thechassis comprises one or more one time twist off tabs for each slot thatextend from the front to the rear of the platform. These twist off tabsare left intact for slots not to be populated with modules. The tabs areremoved for slots to be populated with a module. When removed, thespaced created forms the airflow openings permitting cooling air to flowover the module.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a perspective view illustration of the shutter of the presentinvention having a plurality of cams positioned thereon;

FIG. 2 is a perspective view illustration of the shutter of the presentinvention installed in a platform and which is in the closed position;

FIG. 3A is a perspective view illustration of a portion of a platformwith the shutter of the present invention installed therein in theclosed position and having a PC board not yet inserted;

FIG. 3B is a side view illustration of the shutter in the closedposition corresponding to FIG. 3A;

FIG. 4A is a perspective view illustration of a portion of a platformwith the shutter of the present invention installed therein and with thePC board inserted half way;

FIG. 4B is a side view illustration of the shutter in the half openposition corresponding to FIG. 4A;

FIG. 5A is a perspective view illustration of a portion of a platformwith the shutter of the present invention installed therein and having aPC board fully inserted;

FIG. 5B is a side view illustration of the shutter in the completelyopen position corresponding to FIG. 5A;

FIG. 6 is a perspective view illustration of an example platform with aplurality of modules installed therein and having shutters installed onthe lower rails;

FIG. 7 is a perspective view illustration of an example platform with aplurality of modules installed therein and having shutters installed onthe lower and upper rails;

FIG. 8 is a schematic diagram illustrating the switch circuit forconditional operation of the fan for a single module;

FIG. 9 is a schematic diagram illustrating the switch circuit forconditional operation of the fan for multiple modules; and

FIG. 10 is a diagram illustrating an alternative embodiment of thepresent invention including a one time twist off airflow shutter.

DETAILED DESCRIPTION OF THE INVENTION

A perspective view illustration of the shutter of the present inventionhaving a plurality of cams positioned thereon is shown in FIG. 1. Theshutter, generally referenced 10, is constructed so as to close off theairflow gaps between the rails of a platform, e.g., chassis or cardcage. The shutter 10 is opened by the insertion of a module, i.e., PCBor circuit card, and is closed by the removal of the module via theaction of spring 19. The spring 19 is positioned so to open and closethe shutter with the insertion and removal of a module.

The shutter 10 comprises an elongated substantially flat rigid member 12with a plurality of cams 16 fixed on its upper surface. The shutter 10can be manufactured from any suitable material such as metal or plastic.Depending on the material used, elongated rib 14 may or may not benecessary for increasing the strength of the shutter 10. A pivot, i.e.,pin, 18 on either side of the shutter is normally seated in holesprovided on the front and rear portion of the platform. The spring 19 isalso affixed to the platform so as to maintain the shutter in the closedposition when a slot is unoccupied.

The plurality of cams 16 have an extended rotation ramp 26 having ahelical shape. The ramp begins at near zero incline at the front of theshutter and extends, preferably in a continuous manner, incounterclockwise fashion to substantially the 90 degree point at therear of the shutter.

A perspective view illustration of the shutter of the present inventioninstalled in a platform and which is in the closed position is shown inFIG. 2. Only a portion of the platform (card cage chassis) 20 is shownfor clarity sake. The shutter 10 is shown in the closed position underairflow openings 29. Rail guides 22 are affixed to the surface 28 of thecard cage and positioned on either side of the path of the module.

The shutter 10 is pivotably connected to the front and rear of theplatform 20 via front and rear pivot pins 18. The shutter is mounted inthe platform such that the plurality of cams 16 fit within the railsguides 22 and protrude through the openings 24. The cams must protrudethrough the openings sufficiently to make direct contact with the loweredge of a module as it is inserted into the slot in the platform.

In accordance with the present invention, when the module is firstinserted, it makes contact with the surface 26 of the cam 16 closest tothe front of the platform. Upon further insertion of the module, theforce exerted on the cam pushes the shutter downward as it thus beginsto open. As the module is inserted further into the platform, the actionof the cams 16 increases and the shutter 10 is opened further andfurther. Since the shape of the cams is a helix, the shutter rotatesdownward into the open position. Eventually, when the module is fullyinserted into the platform, the shutter is in its fully open position.At this point, the edge of the module is contacting the rear portion ofthe last cam 16, which has the highest cam action. When the shutter isfully open, air can flow freely through the bottom airflow openings 29across the module and out through complementary airflow openings in theupper portion of the platform. Conversely, when the module is removed,the elastic tension stored in the spring 19 rotates the shutter into theclosed position.

A perspective view illustration of a portion of a platform with theshutter of the present invention installed therein in the closedposition and having a PC board not yet inserted is shown in FIG. 3A. Themodule 30 is shown positioned at the beginning of its travel into theslot in the platform 20. The module 30 comprises a back connector 32 anda front panel 34. The closed shutter seals the airflow openings 29.Shown also are the plurality of cams 16 and their surfaces 26 and slotopenings 24.

A side view illustration of the shutter in the closed positioncorresponding to FIG. 3A is shown in FIG. 3B. In the closed position,the shutter 10 substantially seals the openings 29 in the platform 20.Cams 16 and associated surfaces 26 appear as a ramped surface thatprogresses from the front of the platform to the rear. The pivot 18 isaffixed to a receiving hole in the platform 20.

A perspective view illustration of a portion of a platform with theshutter of the present invention installed therein and with the PC boardinserted half way is shown in FIG. 4A. The module 30 is shown positionedat the midpoint of its travel into the slot in the platform 20. Theairflow openings 29 in the platform 20 are partially open at this pointpermitting less than a maximum flow of air. Shown also are the pluralityof cams 16 and their surfaces 26 and slot openings 24.

A side view illustration of the shutter in the half open positioncorresponding to FIG. 4A is shown in FIG. 4B. In the midpoint position,the shutter 10 has been rotated to an angle of approximately 45 degreesfrom the horizontal closed position. Cams 16 and associated surfaces 26appear as a ramped surface that progresses from the front of theplatform to the rear. The pivot 18 is affixed to a receiving hole in theplatform 20.

A perspective view illustration of a portion of a platform with theshutter of the present invention installed therein and having a PC boardfully inserted is shown in FIG. 5A. The module 30 is shown positioned atthe end of its travel into the slot in the platform 20. The airflowopenings 29 in the platform 20 are fully open at this point maximumairflow through them. Shown also are the plurality of cams 16 and theirsurfaces 26 and slot openings 24.

A side view illustration of the shutter in the completely open positioncorresponding to FIG. 5A is shown in FIG. 5B. In the fully openposition, the shutter 10 has been rotated to an angle of approximately90 degrees from the horizontal closed position. Cams 16 and associatedsurfaces 26 appear as a ramped surface that progresses from the front ofthe platform to the rear. The pivot 18 is affixed to a receiving hole inthe platform 20.

It is important to note that the invention contemplates shutters havingany number of cams. Shutters with three cams was shown for illustrativepurposes only. Once skilled in the art could easily construct platformswith shutters having any number of cams. In each case, however, thesurface of the cam comprises a preferably smooth rotation ramp fromsubstantially zero angle and upwards to higher angles. The cam end pointmust protrude a sufficient amount so as to rotate the shutter from thecompletely closed position to the fully open position.

A perspective view illustration of an example platform with a pluralityof modules installed therein and having shutters installed on the lowerrails is shown in FIG. 6. The platform 40 is shown having a plurality ofslots. Each slot has a lower portion 41 and an upper portion 51. Eachslot on the lower portion comprises guide rails 50 for directing theinsertion of a module. Correspondingly, each slot in the upper portion51 comprises guide rails 53. The lower portion 41 also comprises airflowopenings 46 and shutters 44 which are normally closed while itsassociated slots are unpopulated. Likewise, the upper portion 51comprises airflow openings 52 which are normally always open to the flowof air.

As an example only, the platform is shown populated with two modules 42inserted into the right most slots in the platform. Assuming the modulesthemselves form a seal against the lateral movement of air once insertedinto the platform, no air can flow from the two rightmost openings intothe empty space within the platform. While the two modules 42 are fullyinserted into the slots, their respective shutters are in the fully openstate permitting cooling air to flow from the openings 46 in the bottomportion of the platform, over the surface of the modules and out throughthe openings 52 in the upper portion of the platform. The remainingunpopulated slots remain closed by their shutters, thus preventing airfrom entering the empty space and bypassing the installed modules.

A perspective view illustration of an example platform with a pluralityof modules installed therein and having shutters installed on the lowerand upper rails is shown in FIG. 7. The platform 60 comprises a lowerportion 68 comprising airflow openings 66, guide rails 72 and shutters64. Similarly, the upper portion 70 comprises airflow openings 76, guiderails 70 and shutters 74. Two modules 62 are shown installed in theright most two slots in the platform 60. This embodiment is similar tothat of FIG. 6 with the difference being that shutters are in place onboth lower and upper portions of the platform. Depending on thedimensions of the modules used and the particular application, the uppershutters may or may not be needed, assuming cooling air enters from thebottom and exits through the top. The additional set of shutters foreach slot may be needed to reduce the airflow into the empty spacewithin unpopulated slots in the platform.

Most platforms designed to hold multiple modules, are outfitted with atleast one fan for providing cooling air to be directed across themodule. If a module, however, is not installed in the platform, the fandoes not need to operate as there is nothing to cool. Thus, to conserveelectrical power and increase the life of the fan, a switch mechanism isused to operate the fan only when the module is inserted in the slot. Inaddition, if the shutter of a slot is closed, the necessity for the fanto operate is obviated, as no cooling air is needed.

A schematic diagram illustrating the switch circuit for conditionaloperation of the fan for a single module is shown in FIG. 8. Theswitching is performed via a loopback contact 88 connected to or withinthe connector 82 of the module. The wiring 94 couples the connector 84affixed to the backplane 86 to the fan 90 and the power supply 92. Usingthis arrangement, the fan is operational only when the module 80 isfully inserted into the slot in the platform. In addition, as describedabove, the insertion of the module also opens the shutter permitting theflow of air from developed by the operation of the fan.

A schematic diagram illustrating the switch circuit for conditionaloperation of the fan for multiple modules is shown in FIG. 9. In thecase when a platform is constructed to hold a large number of modules,more than one fan is typically used to provide sufficient coolingairflow for all the modules. In this case, a single fan may beresponsible for providing cooling airflow for a plurality of modules. Inthis case a group of modules located next to each other can beassociated with a single fan. In any one of the modules within the groupis installed, the fan is made to operate. If all slots in the group arenot populated, the fan is to be turned off.

Therefore, it is provided by the present invention means for ORing theinsertion of any of a group of modules to control the operation of oneor more fans. In this example, the group comprises four modules assignedto a single cooling fan 104. The connector 100 of each module is shownmated with the connector 102 on the backplane 112 of the platform.Electrical power from the power supply 106 is applied to the fan 104 viawiring 108 when one or more modules are inserted into the platform. Oneskilled in the art can easily extend his example to groups having anynumber of modules and any number of fans.

An alternative embodiment of the present invention comprises a one timetwist off airflow shutter that is normally in the closed position. Adiagram illustrating an alternative embodiment of the present inventionincluding a one time twist off airflow shutter is shown in FIG. 10. Theplatform 130 comprises front and rear portions 120 with rigid crossmembers 128 connected between them. Note that although only the lowerportion of the platform is shown for clarity sake, this one time twistoff embodiment can be implemented on the upper portion as well.

The cross member 128 comprises a slot rail guide 122 for directing theinsertion of a module. One or more airflow opening tabs 124 are cut intoor stamped from the cross member 128. A thin narrow portion 126 on eachtab connects the tab to the cross member.

In operation, the tabs 124 are left intact on slots that are not to bepopulated by modules. Thus, on these slots, the tabs 124 block anyairflow. On slots that are to be populated with a module, the tabs 124are removed by twisting repeatedly until they break off from thechassis. Once broken off, the tabs typically cannot be easily put backon. Removing the tabs from a slot permits cooling air to flow across themodule inserted therein. This embodiment has utility in applicationswhere it is not likely that modules will be removed from the platformonce they are installed.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

What is claimed is:
 1. A platform for housing a plurality of modules,comprising:a box like chassis open on one face and adapted to acceptsaid plurality of modules, said chassis comprising a plurality of slots,a lower portion and an upper portion; and an electrical fan mechanismproviding cooling airflow to be directed over said modules; wherein eachslot comprises rails for guiding the insertion of one of said modulesinto said chassis; an airflow opening mechanism for allowing air to flowover and across said module inserted into said slot; a shutter pivotallyconnected to said chassis and rotatable between a closed positionwhereby air is prevented from flowing through said airflow openingmechanism and a fully open position wherein maximum airflow is permittedto flow through said airflow opening mechanism; one or more cams affixedto said shutter and operative to rotate said shutter from a closedposition to an open position as a consequence of said module directlycontacting said cams during the insertion of said module; and a springmechanism connected to said shutter and said chassis and operative toretain said shutter in the closed position in the absence of one of saidmodules in said slot, said spring mechanism operative to rotate saidshutter from the open position to the closed position upon the removalof one said modules from said slot.
 2. The platform according to claim1, wherein said electrical fan mechanism comprises a plurality ofelectrical fans.
 3. The platform according to claim 1, wherein saidairflow opening mechanism comprises one or more openings in said lowerportion and said upper portion of said chassis so as to provide airflowacross and over any modules inserted in said slots.
 4. The platformaccording to claim 1, wherein at least a portion of said slots arepositioned adjacent said lower portion of said chassis.
 5. The platformaccording to claim 1, wherein at least a portion of said slots arepositioned adjacent said upper portion of said chassis.
 6. The platformaccording to claim 1, wherein said slots are positioned adjacent thelower and user portions of said chassis.
 7. The platform according toclaim 1, wherein said shutter comprises a substantially rigid elongatedmember extending from the front of said chassis to the rear thereof andis sufficiently wide enough to cover said airflow opening mechanism whenin the closed position.
 8. The platform according to claim 1, wherein atleast one of the one or more cams have a helical surface.
 9. Theplatform according to claim 1, further comprising an electrical contactmechanism which causes said fan mechanism to operate only when saidmodule is fully inserted in said slot in said chassis.
 10. The platformaccording to claim 1, further comprising an electrical contact mechanismwhich causes one or more fans adjacent a group of modules to operateonly any member of said group of modules is fully inserted into saidchassis.